The fiber tip of fibers such as mammalian hair provides a certain stimulus when they touch the surface of the skin, for example by the palm of a hand when treating the fibers, or by neck, shoulder, or chest area, merely based on gravity. Relatively strong stimulus of the fiber tip may be described as stiffness, prickly feel or itchy feel, and is considered a negative sensory feel by some consumers. The force generated by the fiber tip, which is perceived as stimulus, varies depending on the properties of the fiber including, but not limited to, factors such as the roughness of the fiber tip, and the flexibility over the length of the fiber. Usually, the smoother the fiber tip, and the softer the fiber is along its entire length, the lower the force generated upon the fiber tip touching the skin. When the fiber is mammalian hair, stronger fiber tip force or stimulus may be recognized by some consumers as “lack of softness of the hair”, and associated with poor conditions of the hair, such as split ends, dryness, roughness of cuticle, and overall stiffness, brittleness, or inflexibility of the hair. Hair conditioning or hair treatment compositions designed for imparting softness to the hair may alleviate the stimulus generated by the fiber tip by, not only imparting softness to the hair, but also improving such poor conditions. Hence, the unpleasant stimulus, such as stiffness or prickly feel generated by the hair fiber tip, may be considered as a sign of less treated or conditioned hair by consumers who prefer soft hair.
Some consumers have the habit of measuring the softness of the hair by holding a strand of hair from beneath, to sense the prickly feel on the palm. When the prickly feel of pre-conditioned hair fiber tip is reduced after conditioning, consumers who prefer soft hair may assess that the hair has been well conditioned. Such method, however, is subjective and is different depending on the consumer. Methods for objectively measuring the condition of the hair have been proposed, for example by microscopy, or by detecting properties of the surface of the skin such as in U.S. Pat. No. 6,817,222. However, these methods usually require many types of equipment and provide data to be interpreted by the skilled person, while being barely understandable for the general consumer. There remains a need for a method allowing a direct visualization resembling and correlating with the “stimulus sensing” provided by the general consumer.
Based on the foregoing, there is a need for a method allowing a direct visualization of the force generated by the hair fiber tip and thereby allowing a direct visualization of the benefit of a hair care composition for decreasing stimulus generated by the hair fiber tip. In addition, there is a need for a method which can be easily understood by the non-skilled person, including the general consumer and/or the salon stylist. There is also a need for a method for supporting advertising claims about the benefit of a hair care composition for decreasing the stimulus generated by the hair fiber tip. There is also a need for a method for supporting advertising claims about the comparison of the benefit of at least two hair care compositions for decreasing the stimulus generated by the hair fiber tip, and therefore, for making the hair soft. Finally, there is a need for a method of marketing a hair care composition, which composition is capable of decreasing the stimulus generated by the hair fiber tip, and therefore is capable of making the hair soft.